While discussing with some people how to get the Linux kernel to do the
right thing wrt sending output to both the serial console and the
hdmi out / lcd screen when booting on ARM devices, Grant Likely pointed out
that there already is a solution for this.

All we need to do is set the /chosen/stdout-path fdt property, and if no
console= arguments were specified on the kernel commandline the kernel
will honor this and add this device as a console (next to the primary
video output on hdmi).

And u-boot already has support for setting this, all we need to do is
define OF_STDOUT_PATH and then everything will just work ootb, without
people needing to meddle with adding console= arguments in extlinux.conf .

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Reviewed-by: Tom Rini <trini@ti.com>